Devices permitting the cooling of a pressurized-water nuclear reactor after its shutdown following an accident are known. Such devices incorporate, in association with each of the loops of the primary circuit of the reactor, an auxiliary feed circuit for the corresponding steam generator. In this auxiliary circuit a condenser is arranged, connected to both the outlet of the steam generator and to the feed water inlet of this steam generator. When the auxiliary circuit is in operation, the condenser receives steam from the generator and ensures its condensation. The auxiliary circuit condenser may be positioned at a higher level than the settling level of the water present in the steam generator, so that the condensate may be redirected to the steam generator by gravity circulation.
While the reactor is being cooled, the steam leaving the generator is at a high temperature and pressure, both of which can vary during the cooling. This temperature and this pressure are 300.degree. C. and 86.10.sup.5 Pa, respectively, at the beginning of the cooling and 160.degree. C. and 5.8 10.sup.5 Pa at the end of the cooling, just before the cooling circuit comes into operation when the reactor is shut down. Known condensers which are employed, for example, at the outlet of the turbine stages of electrical power stations are not suitable for cooling such steam at a high temperature and high pressure, with condensate recirculation, and other devices have been suggested, such as, for example, condensers immersed in a large volume of stored water. The condensers consist of a distribution and exchange unit incorporating a tube assembly in which the steam circulates. Cooling and condensation of this steam are carried out by virtue of the cooling of the tubes immersed in the stored water. This storage consists of one or more pools arranged in the structure of a building adjoining the reactor containment shell, at a height situated above the steam generators.
This arrangement considerably complicates the design of the nuclear power station buildings and, in the case of some types of power station, it is not even possible to envisage the installation of such pools at a height.
Furthermore, the exchanges between the wall of the tubes and the bulk of water in which these tubes are immersed do not always take place under favorable conditions, although localized boiling of the mass of water in contact with the tubes promotes such exchanges, by virtue of the circulation of the steam produced.
Finally, control of the operation of the condensers immersed in large-volume pools is difficult to implement.
Condensers are also known which are constituted of a water storage vessel in which is immersed a unit comprising generally vertical exchange tubes which are connected each at its upper end to a steam inlet manifold, and at its lower end to a condensate discharge manifold. The water of the storage vessel which can be evaporated is replaced in the vessel. Such a condenser is, however, of a low efficiency, the thermal exchange on the external surface of the tubes not being enhanced by intense circulation of the water of the tank.